This guide contains spoilers for Baldi's Basics Classic Remastered. Proceed on your own risk.

0.0.2.0 - When launching the game with the mod for the first time, you will see the "installation confirmation screen".
0.0.3.0 - Created an installer. Now it's a little bit easier to install the mod.

The game makes A LOT of checks, to make sure you have not beaten null. Once you see the final cutscene and get NULL achievement and the game does something sneaky:

• It grants you NULL achievement.
  
• It changes flags[4] to true in the save file (it's encoded with it's name)
  
• It changes flags[0] to true in the HiScores file (it's encoded with 99)
  
• It changes registry entry DiagInfo_[random string] to 1
  
• It creates a pseudo-random folder in the %userprofile%/AppData/Local/Temp folder

When the game loads your save file, it does this:

• It loads the save file as usual
  
• It runs method named NullCheck()
  
• It checks for the previously stated changes. If at least one passes, the game thinks NULL was beaten and grants you the achievement again.

NullCheck code:

There are two ways to bypass this check:

We need to do the following:

• Decrypt the save file, set flags 4 and 5 to false and encrypt it back.
  
• Decrypt the HiScores file, set flags 0 and 1 to false and encrypt it back
  
• Set registry entry Computer\HKEY_CURRENT_USER\Software\Basically Games\Baldi's Basics Classic Remastered\DiagInfo_[random string] to 0
  
• Remove two temp folders (this is where I got stuck, while I was trying to automate this process)

The last one is really hard to do, because I need to get the same random number generator seed the game does. For somewhat reason, I cannot reuse the same code that the game uses to generate the seed, therefore, I am unable to delete these folders. The only way to get the seed is modifying the game, but we are deliberately trying to avoid doing that.

If we cannot revert all the checks the game makes, why not create a mod that bypasses all of them? When game runs NullCheck method, we can patch it, so it does nothing. It's surprisingly easy to do!

Bypassing null check:

Using the installer (recommended)

You can download the installer here[github.com]

Starting with 0.0.3.0, you can now use the installer to do the process for you. To download it, just click on installer.zip and unpack it.



Antivirus might think that installer is a virus, because it really looks like it. It modifies game folder by adding some unknown third-party software. If it get's triggered by it, just allow it on the device..
If after launching the app you see this window, click show more and then run anyway.



If you did everything right, you will see this window



After that click Open... and select the game folder. If it is valid, you will see something like this



Then click Begin installation procedure and wait for the next popup



After launching the game, recheck again. You should get this message:



Finally, click Begin installation procedure again. You should be done, if you see this message:

Manually

Download BepInEx 5.4.21[github.com] release. You need to download either x64 or x86 (if you are running 32-bit system). If you are using linux, download unix version.


After that, move the contents of the zip file inside the game's directory



After running the game once, close it and head to the mod's release page[github.com] and download latest release.


After downloading the mod, move it inside %gamefolder%\BepInEx\plugins


If you did everything right, you will see this image and hear Baldi say "Wow!" upon loading the main menu.
You will see it only once.

This is easy, just remove BBCR_Return_Null_Mod.dll and you are good to go!

Thanks for reading my guide! I hope it helps. Please leave a like and if you feel particularly generous, give this guide an award!